Sheet metal forming die means



Nov. 27, 1956 c. P. MOGREGOR 2,771,851

SHEET METAL FORMING DIE .MEIANS Filed May 20, 1954 3 Sheets-Sheet 1 l9"w l -26 E54 Nov. 27, 1956 P. MCGREGOR 2 77 SHEET METAL FORMING DIE MEANSFiled May 20, 1954 Sheet 2 F'g.- E

INVENTOR. CLIFTON I? McGREeoR Agent Nov. 27, 1956 c. P. MCGREGOR ,3

SHEET METAL FORMING DIE MEANS Filed May 20, 1954 3 Sheets-Sheet 3 UtlitSHEET-METAL FORMING DIE MEANS Clifton P. McGregor, North Hollywood,Calif., assignor to Lockheed Aircraft Corporation, Burbank, Calif.

Application May 20, 1954, Serial No. 431,090

Claims.- (Cl. 11346) This invention relates to the shaping or forming ofsheet material such as sheet metal, and the like,'and re-'latesmore'particularly to dies for drawing or forming such materials.

In the aircraft industry and related industries, many sheet materialparts are shaped or formed by die sets. A'great many ofsuch parts haveheretofore been formed in dies used in expensive, complicated doubleaction draw presses, the double action presses' being necessary.

to prevent or reduce the development of wrinkles in the marginal orflange regions of the blank-orpart as well as in-the major regionsthereof. Although attempts have been made to control the flow or draw ofthe material into the cavity of conventional drop hammer dies bythesimpler, less costly drop hammer dies and drop' hammers in carryingout-many-of the sheet material forming operations.

It is a general object of the present invention to provide low costsheet material forming diesadapted to be used in drop hammers to formsheet'material parts of the classes or types that have heretofore been,as a general rule, formed in the more expensive draw dies which requiredthe use of complicated, double action draw presses.

Another object of the invention is to providedrop hammer die means ofthe character referred to that effectively control the flow of metal ofthe blank or partduring the drawing or forming operation oroperations'to prevent the development of wrinkles in the part. Inaccordance with the invention, distributed, equal or controlled pressureis exerted on the marginal areas, which may or may not be of substantialextent, of the blank or part during the forming action and thiscontrolled pressure governs the flow of the metal into the die cavity toprevent the development of wrinkles in the part.

Another object of the invention is to provide die means of this kindthatcan be designed and constructed to form parts of different sizes,configurations and depth of draw.

It is another object of the invention to provide drop" hammer dies ofthe character referred to that may be inexpensively produced frominexpensive readily available materials.

It is a further object of the invention to provide drop hammer die meansthat may, if desired, incorporate trimming or blanking means toeffectively trim the part while being securely clamped againstdisplacement.

Other objectives and features of the invention will bcome apparent fromthe following detailed description of States Patent 2,771,851 PatentedNov. 27, 1956 typical preferred embodiments thereof throughout' whichdescriptionreferenceis made to the accompanying drawings' in which':

Figure 1 is a perspective view of a'female die of the invention;

Figure 2 is a fragmentary vertical sectional view of a die set of theinvention'prior to the initial forming stage;

Figure 3 is a view similar to Fig. 2 showing the punch and associatedparts in the position assumed at the end of the first forming stage;

Figure 4 is a" similar view showing the parts prior to the second stageforming operation;

Figure 5 is a similar vertical sectional view showing the parts in thepositions assumed at the end of the second stage forming operation;

Figured is-a vertical sectional view" illustrating the punchandassociated-pa-rts in -the'positions assumed at the end of the finalforming stage;

Figure-6A is a pe'rspective'view ofa pair-of therubber pads; and

Figure 7 is a vertical sectional view of another form of die set'of the"invention incorporating blanking or trimming means.

The die apparatusor die setof the invention illustrated in Figures 1to6A inclusive of the drawings'includes'a die '10,*a-punch'11 carried bythe drop hammer head 'H,

a clamping ring1 2' ass'ociated'with the punch, and yield ing pad means13*arran'ged'between the head H and the ring'12.'

The'die '10is the relatively stationary member or element of the diesetand is secured on the bed of the drop hammer, not shown. Ithas beenfoundmost practical to construct the die "10 of Kirksite although thedie may be formed of any selected or suitable material. The

upper oractiveface14of the die 10 may be of any shape, depending uponthe intended configuration to be given the part-'P. In the 'drawings'thedie face '14 is curved or concave and has'acavity' 15'into which thepart is to be drawn'or formed. Theparticular die 10 illustrated'hasanupstanding rim'ld'around its face 14and the inner surface 17 ofthis-rimslopes or flares outwardly and upwardly.

The punch 11 is secured to 'the underside of the drop hammer head H tomove or travel therewith and its lower portionisdesigned to'conform'with' the die cavity 15. As illustratd'in the drawings, the'side wallsof the cavity 15flare orslope upwardlyandoutwardly and the side surfacesof the punch" 11 are correspondingly inclined; In most cases'it may bepreferred to construct the punch 11"of Kirksite," orthe like; althoughother suitable materials may be used for this purpose. In'thisconnection it may be" notedthat the die 10 and punch 11 are constructed'of substantiallyunyielding materials. The lower face and lower portionof the punch 11 are shaped to mate with the' die 10' and moreparticularly with the cavity 15 with suitable clearance, provisionbeing' made for the thickness of theblank or part P which is to beformed between them. The sides 18 of the punch 11 preferablyslope'upwardlyand outwardly for the purpose which will la'terbecomeapparent. I

The clamping ring 12 is provided to exert a sufficient downwardpressureon the flange or marginal portion 19 of the blank or part P toprevent the formation or developm'ent'of wrinkles in the part as itispushed or drawn into eryof the'punch 11. The'upper end'of the ring '12is" preferably flat'to be parallel with the'lower face of the hammerhead H. The lower face 20 of the ring 12 is shaped to mate with the face14ofthedie 1t and-in the case illustrated, is curved'or convex to besubstantially concentricwith theupper-die-face." The lower end of'th'e'ring 12 has a reentry or groove 21 for receiving the rim 16 of the die10, this groove being shaped to conform with the rim with workingclearance. The inner surface 22 of the ring 12 flares or slopes upwardlyand outwardly at substantially the same angle as the side 18 of thepunch 11 so that when the punch moves downwardly these surfaces 18 and22 cooperate to centralize the ring with respect to the punch. The ring12 is arranged to have relative vertical movement with respect to thepunch 11. Means is provided for limiting this relative movement, thismeans including two or more spaced pins 23 projecting horizontallyinward from the ring and received in vertical slots 24 in the punch 11.The pins 23 and slots 24 are related so that the ring 12 is raised withthe punch when the hammer head 11 is raised, the ring assuming aposition such as shown in Figure 2 and when the punch 11 is moveddownwardly the ring 12 is adapted to move down to first engage theflange 19 of the blank or part P to be thereby held against furtherdownward movement while the punch continues downwardly to draw the blankor part into the die cavity 15.

In accordance with the invention, the clamping ring 12 is formed of amaterial that is yielding or compressible. I have found it mostpractical to construct the clamping ring 12 of a thermo plastic, such ascellulose acetate, cellulose butyrate, or combinations or blendsthereof. The clamping ring 12 preferably has a Shore hardness on the Ascale of between 80 and 100. When the ring 12 is to be constructed of athermo plastic such as above described, it may be expeditiously andinexpensively produced by being cast directly to the punch 11, it beingdesirable to arrange a sheet of metal, plastic, or the like, around thepunch prior to the pouring of the plastic and to employ a parting agentsuch as a high temperature wax. The ring 12, when constructed ofcellulose acetate, cellulose butyrate, or blends thereof is found to beself-lubricating and to act or press on the flange 19 of the part P tocontrol the metal flow without binding or galling. In many cases it maybe found desirable to provide the lower face 20 of the ring 12 with aholding ridge or head 25 and the top face 14 of the die with a companionor mating groove 26, the bead and groove cooperating to assist ingripping or anchoring the flange 19 adjacent its outer margin during thedrawing or forming operations. It will be observed that the ring 12 issomewhat shorter in the vertical direction than the punch 11, to leave aspace above the ring to receive the yielding pads 13.

The pads 13 are arranged between the underside of the hammer head H andtheupper end of the ring 12 to transmit downward movement and force fromthe head to the ring. While the pads 13 may be constructed of anyselected yielding or compressible material, I have found it practical toconstruct them of rubber. The pads 13 preferably have a Shore hardnessof from 50 to 60 on the A scale. It is preferred to employ sectionalpads 13 to facilitate their installation and removal. Thus, as shown inFigure 6A there may be two substantially C- shaped pads 13 arranged inend to end relation to form an assembly capable of surrounding the upperportion of the punch 11. The thickness of the yielding pads 13 isdetermined by the nature of the forming or drawing operation to beperformed and pads of dilferent thicknesses. will often be used duringsuccessive phases of the forming operations. Thus it will be noted thatthe pads 13 employed during the first or initial forming operation arethicker than the pads 13 shown in Figure 4 and used during the second orsuccessive stage of the operations. It will be observed in Figures 2 and4 that the pads 13 and 13 are proportioned so that their inner and outermargins or peripheries are spaced from the adjacent peripheries of theclamping ring 12, thus leaving ample space for the yielding rings toflow or distort laterally.

In performing certain drawing or forming operations it may be desirableto face the active lower portion of the punch 11 with a hard, orrelatively hard material such as a steel or hard plastic to assist thedrawing action. Furthermore, in carrying out certain forming operationswhere the finished part is to have a special or peculiar configuration,metal shims may be installed either above or below the pads 13 or 13 incertain regions of the assembly or the pads 13 may vary in initialthickness. However, as it is usually unnecessary to resort to either thehard facing of the punch, the use of shims or pads of unequal thickness,such details have been omitted from the present disclosure.

In employing the die means of the invention the punch 11, clamping ring12 and pads 13 are assembled under the hammer head H as shown in Figure2 of the drawings, and the blank or part P is arranged in position onthe upper face 14 of the die 10. The drop hammer head H is then loweredor dropped to cause the punch 11 and die 10 to cooperate in forming thepart P. During the sudden downward movement of the punch 11 the clampingring 12 is the first to engage the flange or marginal region 19 of thepart P to clamp the same against the top face 14 of the die 10. The pads13 are compressed at this time to exert or transmit the requiredclamping pressure through the ring 12 to the marginal area of the partP. The punch 11 of course engages and pushes the intermediate portion ofthe part P into the die cavity 15 to draw or form the same. The ring 12,being formed of a yielding material, is vertically compressible duringthe drawing or forming operation to allow and control the radialslippage or flow of the flange area 19 of the part P. Being constructedof a yielding material the clamping ring 12 exerts a uniform or equalpressure resembling an hydraulic pressure throughout the extent of theflange area 19 of the part P to prevent the initiation or forming ofwrinkles in either this flange area or the axially drawn portion of thepart P. In this connection, it may be noted that where the configurationof the finished part P is such that an increased or varied clampingpressure be exerted or transmitted by the clamping ring 12, either thepads 13 may be of increased thickness at a given region or given regionsand/ or metal shims may be installed either above or below the pads atsuch regions. Even in such instances the yielding material clamping ring12 pressed downwardly against the flange area 19 of the part P by thehead H through the medium of the yielding pads 13, applies or exerts adistributed clamping pressure that has been found to prevent theinitiation of wrinkles in the part P. It is believed that this action ofthe yielding material clamping ring 12 results, at least in part, fromthe yielding action of the ring in controlling the radial flow of themetal of the part P.

In a typical forming operation the initial phase or stage describedabove will only partially form the part P to the die cavity 15. If thisis true, the hammer head H is raised and the first yielding pads 13 areremoved to be replaced by the somewhat thinner pads 13. For example, ina given job the thickness of the first pads 13 may be substantially thesame as the depth of the die cavity 15 while the thickness of the secondpads 13* may be equal to, say, one-half or one-third of the depth of thedie cavity 15. With the second pads 13 in place the hammer H is againlowered to carry out the second phase of the forming. Here, again, theclamping ring 12 is the first element to contact the blank or part P andthe ring exerts a somewhat yielding clamping pressure on the flange tocontrol the draw or forming.

of the metal when the punch 11 contacts the same to push or draw it intothe die cavity 15. This clamping action inhibits or prevents-theformation of wrinkles in the part P. A second or third formingoperation, such as just described, may suffice to completely form thepart P. Figure 6 of the drawings illustrates the parts in the positionassumed during a final forming phase in which the yielding pads 13 and13 have been omitted so that the head H directly transmits'the downwardforce to the yielding clamping ring 12. As shown 5 in Figure 6, thepunchll has firitiHyz-formed-the part P to the die cavity 15.

Figure 7 illustrates a blanking or trimming die means incorporating thefeatures of the-invention? In"-- this case there is'a die 30'ofKirksite, or the likeyhaving a cavity 35 andanupper face 39 surroundedby" an upstandingrim'36. In this embodiment of the inventionthemating-punch'may be formed of two -se'c'ti'ons 40and 41, separated by atrimming'collar or blad42. Although this blade 42 may not-be' annular orcontinuous, it will be assumed that'it is of such a configuration. Thelower faces of the punch" sections 40 and 41 are shaped to mate with thecavity 35--and face 39- of the die 30 to cooperate therewith in shapingorlforming the blank B. The punch sections 40"ar1d 41"are'pfeferablyformed of a relatively yielding or compressible material such ascellulose acetate, cellulose butyrate, or a blend of the same.

A second or outer blanking or trimming blade 44 surrounds the outerpunch section 41. The two spaced trimming blades 42 and 44 are securedto a plate 45 of steel, or the like, secured to the underside of thehammer head H. The lower ends or edges of the blades 42 and 44 havebroad beveled or tapered faces and protrude beyond the lower face of thepunch 40-41 to cooperate with abrupt vertical shoulders 46 and 47respectively of the die 30. Inclined faces 60 extend from the lower endsof the shoulders 46 and 47. The trimming blades 42 and 44 may be formedof mild steel, or the like, and their active lower ends may be facedwith layers 48 and 49 respectively of a hard material such as afiberglas fabric laminated with a hard epoxy resin binder. When thehammer head H is lowered or dropped these hard-faced blades 42 and 44cooperate with the shoulders 46 and 47 of the die 30 to shear or cutthrough the blank B and thus trim the same.

The die assembly of Figure 7 further includes a clamping ring 32 aroundthe outer trimming blade 44, the lower end of this ring 32 is shaped tomate with the face 39 and rim 36 of the die 30 so as to clamp the flangeor marginal area of the formed blank B against the die. The clampingring 32 is formed of a yielding or somewhat compressible material suchas cellulose acetate or cellulose butyrate so as -to exert asubstantially uniform or distributed clamping pressure on the blank B.The punch sections 40 and 41 and the clamping ring 32 may be formed of athermo plastic such as just described having a Shore hardness of from 80to 100 on the A scale. One or more pads or layers 51 of yieldablecompressible material, such as perforated rubber, are arranged betweenthe mounting plate 45 and the upper ends of the punch sections 40 and 41and the clamping ring 32. These pads 51 preferably have a Shore hardnessof from 50 to 60 on the A scale and yield or compress to a considerableextent in transmitting the downward forces from the plate 45 to thepunch and clamping ring.

It has been found that in the operation of the trimming die means shownin Figure 7 the yielding material clamp ring 32 exerts a distributedcontrolled clamping pressure on the marginal or flange portion of theblank or part B during operation. In Figure 7, the yieldable punchsections 40 and 41 and ring 32 being formed of yieldable material andbeing backed up by the pads 51 serve to clamp against the blank B andhold it tightly against the die at both sides of each trimming blade 42and 44. Further, the extensive or broad tapered faces 60 adjacent theabrupt shoulders 47 and the tapered ends of the blades 42 and 44 serveto assist in holding the part or blank against movement during thetrimming operation.

It is to be understood that the particular forming die means illustratedin the accompanying drawings are typical of the invention and arecapable of considerable variation and modification to adapt them for thedrawingior forming of blanks orparts ;of different materials and ofspecial or different configurations; While I have described the diemeans employed in a drop hammer, it may be used in a double actionpress-Yin which case the pads=13 and 13 and the pins 23 are preferablyincombination; a diehaving a' cavity and a surface around thecavityadapted-to,- support a sheet material part, an actuating hammer movabletoward the die, a-

punch on the hammer movable against the part to draw the same into thecavity, a ring of compressible material around the punch and engageablewith the portion of the part resting on said surface, the material ofthe ring having a Shore hardness of between and on the A scale, andyieldable means engaged between the hammer and the ring transmittingsaid movement of the hammer :to the ring to cause the ring to clamp saidportion against said surface prior to and during the engagement of thepunch with the part to control said drawing of the part.

2. Die means for forming sheet material comprising, in combination, adie having a cavity and a surface around the cavity adapted to support asheet material part, an actuating hammer movable toward the die, a punchon the hammer movable against the part to draw the same into the cavity,a ring around the punch engageable with the portion of the part restingon said surface and constructed of a thermo plastic having a Shorehardness of between 80 and 100 on the A scale, means connecting the ringwith the punch for limited axial movement with respect thereto, andyieldable pad means engaged between the hammer and ring transmittingsaid movement of the hammer to the ring to cause the ring to clamp saidportion against said surface prior to and during the engagement of thepunch with the part to prevent wrinkling of said portion.

3. Die means for forming sheet material comprising, in combination, adie having a cavity and a surface around the cavity adapted to support asheet material part, an actuating hammer movable toward the die, a punchon the hammer movable against the part to draw the same into the cavity,a ring around the punch engageable with the portion of the part restingon said surface and constructed of a cellulose acetate having a Shorehardness of between 80 and 100 on the A scale,.means connecting the ringwith the punch for limited axial movement with respect thereto, andyieldable pad means engaged between the hammer and ring transmittingsaid movement of the hammer to the ring to cause the ring to clamp saidportion against said surface prior to and during the engagement of thepunch with the part to prevent wrinkling of said portion.

4. Die means for forming sheet material comprising, in combination, adie having a cavity and a surface around the cavity adapted to support asheet material part, an actuating hammer movable toward the die, a punchon the hammer movable against the part to draw the same into the cavity,a ring around the punch engageable with the portion of the part restingon said surface and constructed of a cellulose butyrate having a Shorehardness of between 80 and 100 on the A scale, means connecting the ringwith the punch for limited axial movement with respect thereto, andyieldable pad means engaged between the hammer and ring transmittingsaid movement of the hammer to the ring to cause the ring to clamp saidportion against said surface prior to and during the en- 7 gagement ofthe punch with the part to prevent wrinkling of said portion.

5. Die means for forming sheet material comprising, in combination a diehaving a cavity and a surface around the cavity adapted to support asheet material part, an actuating hammer movable toward the die, a punchon the hammer movable against the part to draw the same into the cavity,a ring around the punch engageable with the portion of the part restingon said surface and constructed of a cellulose acetate having a Shorehardness of between 80 and 100 on the A scale, means connecting the ringwith the punch for limited axial movement with respect thereto, andyieldable rubber pad means engaged between the hammer and ringtransmitting said movement of the hammer to the ring to cause the ringto clamp said portion against said surface prior to and during theengagement of the punch with the part to prevent wrinkling of saidportion.

References Cited in the file of this patent UNITED STATES PATENTS NortonSept. 20, 1892 Asche Sept. 17, 1901 Moran Jan. 28, 1941 Frey June 8,1943 Egli Nov. 13, 1945 Bruderlin June 24, 1947 Ames Apr. 27, 1948 LedelJune 20, 1950 FOREIGN PATENTS Germany Sept. 19, 1933 Switzerland June16, 1941

